This variant is quite simple but the game play it introduces is sophisticated and games can lead to very many tactical opportunities. All rules inherit from standard chess, with the addition of one simple rule. You can play it in normal games, casual or rated, and in tournaments.
The winning move has to be legal, e.g. you can not give the third check while in check. Checkmating your opponent is still a legal way to win.
A move is considered to give ONE check if the King is threatened, regardless if multiple pieces are giving the check (in the event of a double check).